Google Plus credentials for application Login -

i creating app , want confirm user using google credentials in java environment. can done using google api not sure how code servlet.

i found code snippet authorize credentials authorizationcodeinstalledapp() throwing error , not sure api use.

private static credential authorize() throws exception {     // load client secrets     googleclientsecrets clientsecrets = googleclientsecrets.load(json_factory,         new inputstreamreader(test.class.getresourceasstream("/client_secrets.json")));     if (clientsecrets.getdetails().getclientid().startswith("enter")         || clientsecrets.getdetails().getclientsecret().startswith("enter ")) {       system.out.println(           "enter client id , secret https://code.google.com/apis/console/?api=plus "           + "into plus-cmdline-sample/src/main/resources/client_secrets.json");       system.exit(1);     }     // set authorization code flow     googleauthorizationcodeflow flow = new googleauthorizationcodeflow.builder(         httptransport, json_factory, clientsecrets,         collections.singleton(plusscopes.plus_me)).setdatastorefactory(         datastorefactory).build();     // authorize     return new authorizationcodeinstalledapp(flow, new localserverreceiver()).authorize("user");   } 

hope can me , let me know process it'll great...

if writing servlet run under google appengine, much easier that.

import com.google.appengine.api.users.user; import com.google.appengine.api.users.userservice; import com.google.appengine.api.users.userservicefactory;  ...  @override public void doget(httpservletrequest req, httpservletresponse resp)       throws ioexception, servletexception {   userservice userservice = userservicefactory.getuserservice();   user currentuser = userservice.getcurrentuser();   if (currentuser == null) {     resp.sendredirect(userservice.createloginurl(req.getrequesturi()));   }   else {     // show view   } }